The present invention relates to an apparatus for rotarily punching holes in webs of paper or similar material. Punched webs are used quite generally in business machines, calculators, and the like, the web being usually of paper wound in roll formation and having one or both of its side margins perforated throughout the length of the web. The perforations are usually in line formation marginally of the web, and may be equally spaced apart. It is highly desirable that the perforations be accurately formed with clean, sharply cut edges free of burrs, and that the perforating operation be capable of high speed performance without interruption.
It is generally known that best results in the perforating of paper webs is otained by eliminating shearing action between a counter-rotating punch and die arrangement as the web is passed therebetween. That is, the cutting edge of the punch should preferably meet the cutting edge of the die in exact parallelism at opposite faces of the web, so that removal of material at the perforation is instantaneous all around the edge of the perforation, rather than being progressive, as the term shearing is intended to imply. The matter of eliminating shear in perforating paper webs at high speed has been complicated by the fact that high speed operation requires use of the rotary method, which involves feeding the web between oppositely rotating high speed rolls or wheels carrying complimentary radial punches and dies which, by reason of accuracy of the wheel peripheries, are naturally induced to shear rather than press-cut, as the punches roll accurately into the die openings to produce the hole perforations.
Previous efforts to eliminate shear in perforating by the rotary method have included the use of highly complicated and expensive oscillatory mounts for the punches and dies, built into the rolls or wheels which carry them, and actuated by various complex systems of cams, levers, and other mechanical elements geared to the operating mechanism of the apparatus. The prior devices were extremely heavy and expensive, required the employment of intricate parts in great numbers, and were very difficult to service, lubricate, and adjust within the confines of the wheels or rolls. Such devices were subject to many other objections, not necessary to here relate.
It is most essential that the punched holes be not only accurately spaced but accurate in outline. One particular problem has been with respect to "hangers"; that is, incompletely punched out pieces which remain hanging on the web of paper. This is highly objectionable in that it interferes with the operation of high speed computers and expensive business machines; interferes with certain devices which are used for assembling a plurality of sheets after they leave the printing machine; and is objectionable in appearance so that even though the punched holes no longer have any function after they reach the customer, it would be undesirable to leave them in the assembled business forms.
It is conventional when using equipment embodying the shearing principle, to use say ten or more flat headed punches secured to and extending radially from the periphery of a driven roll. Unfortunately, in time these punches become deformed so that a "half moon" elevated ridge is formed on the trailing edge of the punch. Although I do not wish to be limited thereto, I believe that the abnormal elevation formed on the trailing edge portions of the punches is caused by one or more of the following: by shearing contact of the punch with the harder mating die upon leaving the cavity of the latter; abrasion against paper stock; chemicals in the paper and paper coatings; and difference in circumference of the punch ring to the circumference of the die ring.
While the punches themselves are not individually expensive, to replace or refinish them means shutting down the entire printing and punching apparatus for about twenty to thirty minutes say once in about eight hours. This adds up to considerable expense for down time and labor. One previous way of attempting to eliminate this down time was to tap the punches with a hammer to eliminate the "half moon" ridge, but this rapidly resulted in cutting down the length of the punch so that deficient punching resulted.
Another proposed solution relates to a means for continuously leveling or ironing down elevations in the flat headed punches as soon as they occur and while the machine is in operation in a continuous process by what might be described as "policing means." This means comprises an idler roll mounted on an arm secured to a shaft parallel to the shaft which carries the punch roll. The arm is adjustably mounted and in use is adjusted so that the roller which it carries comes in contact with the punches only when the elevation in a surface occurs. However, it can easily be seen that this increases cost and complexity, has non-uniform results, and is a short lived solution.
Other methods have also been employed in order to reduce the frequency of hanging punches, including tool smoothing attachments operatively associated with the basic hole punching machine. Also utilized are supplementary devices known as "ironers," and improved smoothing tools, including hammers and wrenches. Whether they have been as sophisticated and expensive as the former, or as simple as the latter, these tools attempt to flatten out the punch such that it maintains full circular contact with the die as the punch enters and leaves the die cavity. Unfortunately, full circular contact is often not possible with conventional punches, which have flat heads, since the flattened punch often becomes formed in such a manner that a "half-moon" top results.
Various solutions to the foregoing have been proposed, with one being to increase the penetration depth of the flat punch into its cavity. However, this usually results in faster wearing punches with the consequent increase in downtime while the punches are being replaced. It is important to note that the procedure of increasing punch depth does not solve the detrimental shearing action associated with the punch entering the die cavity.
It is to solve the problems associated with the use of conventional flat head punches that I have evolved a novel dome head punch.